This invention relates generally to computer networks and, more particularly, to networks that employ an access protocol referred to as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). One widely used CSMA/CD protocol is commonly known as Ethernet. The CSMA/CD protocol is defined in ANSI/IEEE Std. 802.3, published by the Institute of Electrical and Electronics Engineers, Inc., 345 East 45th Street, New York, N.Y. 10017, and referred to in this specification as "the IEEE standards."
Under the CSMA/CD rules for access to a network bus or cable, which will be referred to as the channel, any node or station wishing to transmit must first "listen" to make sure that the channel is clear before beginning to transmit. All nodes on the network have equal priority of access and may begin transmitting as soon as the channel is clear and a required inter-packet delay has elapsed. However, if a first node that has started transmitting detects a "collision" with a transmission from another node, the first node continues transmitting for a short time to make sure that all nodes wishing to transmit will detect the collision. Every other node detecting the collision also continues to transmit for a short time. Then each node that has detected a collision terminates transmission of the packet or frame. The nodes involved in the collision wait for the required interpacket delay and then select random, and therefore usually different, delay times, referred to as backoff times, before trying transmission of the same packet again.
The IEEE standards permit station equipment (or data terminal equipment, DTE) to be defined to include an integral media attachment unit (MAU) for connection to a commonly used medium, such as a twisted-pair medium. In the IEEE standards, this mode of operation with a twisted-pair medium is referred to as 10BASE-T operation (pronounced ten-base-tee), and the connector for coupling to the twisted-pair medium is referred to as a 10BASE-T connector. The prefix "10" in 10BASE-T refers to the nominal transmission rate of 10 megabits per second (Mbps). This transmission rate has been adequate for most network users and continues to be adequate for many. However, as the number of personal computer (PC) users added to networks continues to increase, and the computing power of PCs also increases, there is a greater demand for higher speeds in PC-based local area network (LAN) applications. The IEEE 802.3 standards committee has published a new proposed standard that will operate at 100 Mbps. It will be known as the Fast Ethernet and, for connection with twisted-pair networks, will use the term 100BASE-T. The 100BASE-T system has the advantage of providing ten times the speed without change of existing conductors in already established networks, and without major change in existing design. The new standard is based on the same proven CSMA/CD Media Access Control (MAC) protocol layer that is the core of the 10 Mbps Ethernet.
During a period of introduction of the new 100 Mbps standard, and probably for some time to come, there will be a mix of the old and new standards. When connecting a station to a network repeater, some technique must be provided to ensure that they are using the same protocol, i.e. 10 Mbps or 100 Mbps. If a 100 Mbps station transmitter is connected to a 10 Mbps repeater, the 10 Mbps network can suffer severe performance degradation. Switching implementations that have been proposed typically require that transmit and receive operations be shut down to allow switching from one speed of operation to the other. For example, transmit and receive queues need to be initialized after switching. This may also cause some system degradation in the form of loss of message packets.
A new proposed IEEE Standard (802.3 u) specifies an automatic configuration protocol known by the name NWay. The NWay protocol is a physical layer signaling protocol for configuration advertisement and negotiation between two stations at opposite ends of a link segment of a network. The protocol allows a device to advertise its modes of operation to a remote device, and to detect the capabilities of the remote device. Each device uses a fixed, standardized priority list of capabilities, so that the two devices can select a common mode of operation. A series of "link pulses" are used to transmit configuration information and for negotiation of an agreed protocol. A custom chip is needed to implement the NWay protocol and the chip must be installed in both devices at the ends of a link segment.
Other automatic configuration interfaces include the Intel 10/100 PCI Adapter and the 3Com 10/100 PCI Adapter, which appears to be similar to the Intel design. No published literature is available for these products, but they both appear to suffer significant drawbacks in comparison with the present invention.
It will be appreciated from the foregoing that there is still a need for an autoconfiguration protocol that chooses between normal and high-speed transmission rates automatically, with minimal system degradation and minimal packet loss. The present invention is directed to these ends.